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Versions: 00 01 02                                                      
Network Working Group                                    Martin Hamilton
INTERNET-DRAFT                                   Loughborough University
Expires May 1997                                         Renato Iannella
                                                            DSTC Pty Ltd
                                                              Jon Knight
                                                 Loughborough University
                                                           November 1996

       Representing the Dublin Core within X.500, LDAP and CLDAP

                  Filename: draft-hamilton-dcxl-00.txt

                          Status of this Memo

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   The Dublin Core is a simple resource description format which arose
   out of a loose grouping of "librarians, archivists, humanities
   scholars and geographers, as well as standards makers in the
   Internet, Z39.50 and Standard Generalized Markup Language (SGML)
   communities" [1].

   This document describes a mapping from the abstract model of the
   Dublin Core to the X.500 [2], LDAP [3], and CLDAP [4] directory
   service protocols.

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1. The Dublin Core in X.500, LDAP and CLDAP

   We propose that each of the thirteen elements of the Dublin Core be
   made into an X.500/[C]LDAP attribute, and that these attributes be
   gathered together in an object class:

      Name:             dcObject
      Description:      object containing the Dublin Core attributes
      OID:              lutObjectClass.1 (
      SubclassOf:       top
      MayContain:       dcSubject, dcTitle, dcAuthor, dcPublisher,
                          dcOtherAgent, dcDate, dcObjectType,
                          dcForm, dcIdentifer, dcRelation, dcSource,
                          dcLanguage, dcCoverage

   Attribute definitions for the individual Dublin Core elements:

      Name:             dcSubject
      Description:      The topic addressed by the work
      OID:              lutAttributeType.1 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcTitle
      Description:      The name of the object
      OID:              lutAttributeType.2 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcAuthor
      Description:      The person(s) primarily responsible for the
                          intellectual content of the object
      OID:              lutAttributeType.3 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcPublisher
      Description:      The agent or agency responsible for making the
                          object available
      OID:              lutAttributeType.4 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

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      Name:             dcOtherAgent
      Description:      The person(s), such as editors and transcribers, who
                          have made other significant intellectual
                          contributions to the work
      OID:              lutAttributeType.5 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcDate
      Description:      The date of publication
      OID:              lutAttributeType.6 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcObjectType
      Description:      The genre of the object, such as novel, poem, or
      OID:              lutAttributeType.7 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcForm
      Description:      The physical manifestation of the object, such as
                          Postscript file or Windows executable file
      OID:              lutAttributeType.8 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcIdentifier
      Description:      String or number used to uniquely identify the object
      OID:              lutAttributeType.9 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcRelation
      Description:      Relationship to other objects
      OID:              lutAttributeType.10 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcSource
      Description:      Objects, either print or electronic, from which this

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                          object is derived, if applicable
      OID:              lutAttributeType.11 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcLanguage
      Description:      Language of the intellectual content
      OID:              lutAttributeType.12 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

      Name:             dcCoverage
      Description:      The spatial locations and temporal durations
                          characteristic of the object
      OID:              lutAttributeType.13 (
      Syntax:           DirectoryString
      SizeRestriction:  None
      SingleValued:     False

2. Examples and implementation considerations

   For example, using Quipu [5] EDB notation, a Dublin Core "Title"
   element which had the value "Cities of The Red Night" would be
   represented as the attribute/value pair:

     dcTitle= Cities of The Red Night

   One aspect of the Dublin Core does not translate directly to X.500
   and LDAP - each element may have additional qualifying "scheme" and
   "type" information attached to it.  This gives the creator of the
   record a way of indicating additional semantics, e.g. the
   classification scheme being used in the "Subject" element.

   Since X.500 and LDAP are, like most Internet based search and
   retrieval protocols, attribute/value oriented, it is necessary to
   find a place to put this extra information.  We propose that, given
   the difficulty of incorporating this model within the X.500/LDAP
   paradigm, a simple but sub-optimal approach be taken - with any
   qualifying information being placed at the beginning of the value
   part of the attribute/value pair, delimited using round brackets, and
   with any additional qualifiers following using comma separation.

   For example, if the subject classification for the above book were
   813 in the Dewey Decimal system, the resulting Dublin Core record
   expressed as an X.500 EDB entry would look like this:

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     dcSubject= (scheme=DDC) 813

   and a sample "Relation" element, with a "type" qualifier, would look
   like this:

     dcRelation= (scheme=URI, type=isParentOf) http://www.w3.org/

3. Extensibility

   It is important to note that the Dublin Core element set is intended
   for use in describing document-like objects, and not as a means of
   describing arbitrary objects.  Furthermore, the number of elements is
   strictly limited in the interests of interoperability.

   Work is ongoing on the Warwick Framework [6], which attempts to
   provide a mechanism for packaging together collections of descriptive
   information.  It is envisaged that this would be used in cases where
   the Dublin Core element set did not provide enough descriptive
   capability.  This is a subject for further study.

4. Security considerations

   This proposal does not introduce any new security related issues.

   One of the main uses to which the Dublin Core is expected to be put
   is in the generation of author supplied cataloguing information for
   on-line resources.  Implementations which manipulate externally
   produced data should treat it with caution - for example, to avoid
   buffer overrun problems and unexpected evaluation of metacharacters.

5. Conclusions

   This document has shown how the X.500 protocol, and the related LDAP
   and CLDAP protocols, may be used as carriers for the abstract
   resource descriptions of the Dublin Core proposal.

   It should be apparent that a little care is necessary when delivering
   this information via these protocols, but that this does not imply
   any great additional implementation complexity.

6. Acknowledgements

   Thanks to Hoylen Sue, CiTR Pty Ltd (Australia), Rachel Heery and
   Lorcan Dempsey for their comments on draft versions of this document.

   This work was supported by UK Electronic Libraries Programme (eLib)
   grant 12/39/01, the European Commission's Telematics for Research
   Programme, grant RE 1004, and the Cooperative Research Centres

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INTERNET-DRAFT                                             November 1996

   Program, through the Department of the Prime Minister and Cabinet of

7. References

     [1]         S. Weibel.  "Metadata: The Foundations of Resource
                 Description", D-Lib Magazine, July 1995.

     [2]         C. Weider, J. Reynolds, S. Heker.  "Technical Overview
                 of Directory Services Using the X.500 Protocol", RFC
                 1309.  March 1992.

     [3]         W. Yeong, T. Howes & S.  Kille.  "Lightweight Directory
                 Access Protocol", RFC 1777.  March 1995.

     [4]         A. Young.  "Connection-less Lightweight Directory
                 Access Protocol", RFC 1798.  June 1995.

     [5]         S.E. Kille.  "Implementing X.400 and X.500: the PP and
                 QUIPU systems", Artech House, 1991.

     [6]         L. Dempsey, S. Weibel.  "The Warwick Metadata Workshop:
                 A Framework for the Deployment of Resource Descrip-
                 tion", D-Lib Magazine, July/August 1996.

8. Authors' addresses

   Martin Hamilton
   Department of Computer Studies
   Loughborough University of Technology
   Leics. LE11 3TU, UK

   Email: m.t.hamilton@lut.ac.uk

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INTERNET-DRAFT                                             November 1996

   Renato Iannella
   Research Data Network CRC
   DSTC Pty Ltd
   Gehrmann Laboratories
   University of Queensland

   Email:  renato@dstc.edu.au

   Jon Knight
   Department of Computer Studies
   Loughborough University of Technology
   Leics. LE11 3TU, UK

   Email: j.p.knight@lut.ac.uk

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